Printing plate



April 28, 1964 o, Ac V 3,130,670

PRINTING PLATE Filed Feb. 25. 1961 FIG. 2

INVENTOR. EDGAR 0. MACY ATTK United States Patent 3,130,670 PRINTING PLATE Edgar O. Macy, Stow, Ohio, assignor to The B. F.

Goodrich Company, New York, N.Y., a corporation of New York Filed Feb. 23, 1961, Ser. No. 91,041 8 Claims. (Cl. 101376) This invention relates to a printing plate and pertains more particularly to a flexible resilient printing plate which although molded flat curls as it cools from the molding temperature in a direction awayfrom the printing face thereof whereby the printing plate has an inherent tendency to assume the curved contour of the plate cylinder of a rotary printing press.

For many applications it is desirable to provide a flexible resilient printing plate which can be shaped manually to conform to the curved surface of the plate cylinder (sometimes called the application cylinder) of a rotary printing press and can be secured to such curved surface with an adhesive or adhesive coated tape. The design or impression intended to be printed is embodied in the printing surfaces of the printing plate and as the plate cylinder of the printing press revolves ink is applied to the printing surface of the printing plate which then is impressed against the paper upon which the design is to be printed. When a design involving several colors is desired, a series of printing plates, each having a different area of the design raised to contact the paper, is used. Each of the printing plates, accordingly, is responsible for impressing a different area of the design, and has a different colored ink applied thereto. The composite impression realized by the series of printing plates is the desired multi-colored design. It will be appreciated that to obtain good register in the multi-colored impression the printing face of each of the printing plates of necessity must be constructed to close tolerances and must retain dimensional stability during the entire life of the printing plate.

The construction of the flexible resilient printing plates which have been used heretofore commercially consists of a laminate of rubber reinforced with a woven cotton fabric. Specifically, the printing plate heretofore employed comprised a rubber facing layer into which the design to be printed was embodied, a woven cotton fabric to impart reinforcement and dimensional stability to the construction, and a rubber backing layer (which normally was a thinner layer than the facing layer) to impart additional body and durability to the printing plate. In forming this particular printing plate, the rubber facing compound was sheeted and placed in a mold against a face of the mold which was provided with the appropriate deisgn to be embodied in the printing surface of the facing layer of the printing plate, and was partially cured under pressure. The mold then was opened and the woven cotton fabric reinforcement which previously had had the layer of backing compound vulcanized thereto was placed in the mold with the fabric surface positioned against the layer of partially cured facing compound. The mold once again was closed and the assembly was heated under pressure until the facing compound received an optimum cure. During this final heating under pressure, the woven cotton fabric reinforcement was securely bonded to the facing layer. A printing plate so constructed, however, has certain inherent disadvantages which have been somewhat bothersome to the users of this type of printing plate. Specifically, although the printing plate is molded flat, upon cooling the printing plate curls toward the face of the printing plate on which the design is molded. Thus, when the printing plate is adhered to the cylindrical surface of the'plate cylinder of a rotary printing press, the printing plate tends to curl away from such surface and in actual -use has pulled free of the plate cylinder even when the best adhesives or tapes designed for adhering such printing plates to the plate cylinder have been used. When this happens, the printing operation must be shut down and the printing plate re-adhered to the plate cylinder, an annoying and costly incident.

In addition to the adhesion problem mentioned above, the forcing of the printing plate from a curvature in one direction to a curvature in the opposite direction in order to adhere the printing plate to the plate cylinder of the printing press occasions some distortion of the design molded into the surface of the face compound of the printing plate. While some distortion may not be objectionable when single color printing is to be performed, improper register frequently is experienced when a multicolor impression is to be produced.

From the above considerations, it is abundantly clear that some means for eliminating the tendency for printing plates of this type to curl toward the printing face of the plate would be extremely beneficial.

Some attempts to eliminate these difficulties have been made but have not been too successful. One such attempt involves the use of a flat metal backing member to prevent the printing plate from curling upon being cooled from the molding temperature. Such a construction, however, has not provided a satisfactory solution to the problem because of the difficulty encountered when endeavoring to deform the metal backing plate to the curved contour of the surface of the plate cylinder of the printing press, it being almost impossible to bend the metal sheet into a smooth-curved shape. Molding the metal plate initially to a curved contour is objectionable in view of the different sizes of plate cylinders which normally would be encountered even in only a moderate size printing establishment. The use of a perforated metal backing plate has offered no great advantage over an unperforated metal sheet since the perforated metal sheet, like the unperforated sheet, is extremely difficult to form into a' smooth curved contour, the perforated metal sheet tending to bend more readily along the rows of perforations. Woven metal wire (screening) has not been successfully employed since it either is so flexible as to not prevent the curling of the printing plate toward the printing surface or, if sufficiently sturdy to eliminate such curling, is difiicult to conform to the smooth-curved surface of the plate cylinder.

The present invention, however, provides a printing plate which possesses all of the desirable characteristics of the rubber and fabric type of printing plate discussed above and, also, not only does not tend to curl toward the printing face of the plate but rather curls in the opposite direction, i.e. toward the layer of backing material. As a consequence, the printing plate inherently tends to assume the curved contour required for adhering it to the curved surface of the plate cylinder of the printing press. The printing plate made in accordance with this invention, therefore, does not tend to pull away from the plate cylinder to which it is adhered and the impression embodied in the printing face thereof is not subject to objectionable distortion as a result of being deformed from a curvature in one direction to a curvature in the opposite direction. The curvature away from the printing surface of the printing plate is achieved by molding the various components of the printing plate together in a single molding operation (instead of the two-step molding procedure previously used) and by employing in the formation of the backing layer an elastomer composition which has a higher modulus of elasticity than the composition used in the facing layer.

As indicated above, by using a rubber composition in the backing layer which has a higher modulus than the rubber composition used in the facing layer and by using a dimensionally stable fabric reinforcement between the facing layer and the backing layer and by laminating the various components of the printing plate together in a single molding step, the printing plate inherently will curl toward the backing layer rather than toward the printing face of the plate. The reason for this result is that the forces tending to cause thermal shrinkage are stronger in higher modulus rubber compositions than in a rubber composition of less modulus. Thus, with a dimensionally stable reinforcing layer interposed between the facing' layer and the backing layer preventing overall strinkage of the printing plate the rubber composition in the backing layer will undergo thermal shrinkage upon cooling from the molding temperature in preference to the rubber composition in the facing layer and in so doing will cause the printing plate to curl in the desired direction.

The facing layer and backing layer may contain as the elastomer component thereof any elastomeric material just so long 'as the modulus of the composition used in the backing layer is greater than that of the composition used in the facing layer. Thus, either natural rubber or synthetic rubbers can be used in the facing layer and in the backing layer. The modulus of an elastomeric composition is a measure of the amount of pull in pounds per square inch required to stretch a test piece of the composition to a specified elongation. The measurement actually expresses resistance of the elastomer vulcanizate to extension. The common procedure used to measure the modulus of an elastomeric material is described in A.S.T.M. designation No. D 41251T.

Certain elastomers inherently have a higher modulus than other elastomers. Thus, the elastomer composition used in the backing layer and facing layer can be the same except for the elastomer component of the compositions, a higher modulus elastomer being used in the backing layer composition. The modulus also can be varied by compounding. Thus, the same elastomer can be used in both the backing layer and the facing layer but by a judicious selection of the amounts and kinds of compounding pigments used a backing layer composition can be formed which has a higher modulus than that of the facing layer composition. The fact that certain elalstomers inherently possess different modulus properties than other elastomers and that the modulus of an elastomer can be changed by judicious compounding is so well known to the rubber compounder that 13. detailed discus sion thereof is not deemed necessary. In selecting the elastomer which is to be used in the facing layer of the printing plate, it should be remembered that the composition of the facing layer will be the one to which the ink is to be applied and that a composition should be used which will not objectionably be affected by the particular ink to be used.

The facing layer of the printing plate normally is thicker than the backing layer since it is the facing layer which is subjected to wear when the printing plate is in use. Usually, the facing layer of the printing plate has a thickness from .050 to .187 inch while the backing layer has a thickness from 0.010 to 0.100 inch.

The fabric reinforcement used in the printing plate must have suificient dimensional stability (thermal) so that it does not shrink appreciably after being cooled from the molding temperature at which the printing plate is formed. For the purpose of this invention a fabric is considered to be dimensionally stable to heat if it has a shrinkage of less than 0.001 inch per inch length upon being cooled to room temperature after being heated to a temperature of 350 F. The term dimensionally stable fabric used in this application is intended to refer to a fabric which will meet the above specification. The fabric reinforcement may be either a fibrous mat or a woven fabric and may be made from any fiber which has sufficient strength and heat resistance to withstand the molding operation. For example, the fabric reinforcement layer may be made of a polyester fiber such as Dacron fiber (sold by E. I. du Pont de Nemours & Co), Fortrel fiber (sold by Celanese Corporation of America), Vycron fiber (sold by Bea-unit Mills, Inc.) and Kodel fiber (sold by Eastman Chemical Products, Inc.) from nylon fiber, from acrylic fibers such as Orlon fiber (sold by E. I. du Pont de Nemours & Co.) and Verel fiber (sold by Eastman Chemical Products, Inc.), and from refractory fibers such as glass fibers. Glass fiber fabrics are particularly desirable for use as the fabric reinforcement layer of the printing plate because of the extremely high strength of glass fibers (often exceeding 1,000,000 pounds per square inch) and because of the excellent resistance to heat which such fibers exhibit.

If desired, the fabric reinforcement may be treated with an adhesive to assist the bonding of the fabric to the facing layer and the backing layer of the printing plate. For example, the fabric may be dipped into a water dispersion of resorcinol formaldehyde and natural rubber latex before being plied with the backing layer and the facing layer. To insure a good bond between the fabric reinforcing layer and the facing and backing layers, the fabric preferably is frictioned with an unvulcanized elastomeric composition which will bond through vulcanization to the elastomeric compositions used in the backing and facing layers. A neoprene rubber composition frequently is used for this purpose. The frictioning of the fabric with the elastomeric composition can be accomplished on a three-roll calender in the customary manner. Preferably, the separation between the two rolls between which the frictioning actually takes place is approximately just equal to the thickness of the fabric so that only the interstices of the fabric are filled with the elastomeric composition. Also, the center roll (the one which carries the elastomeric composition) preferably revolves at a speed slightly greater than the roll carrying the fabric.

The backing layer preferably is calendered onto the fabric reinforcing layer before these com onents are placed into the mold. The calendering operation can be effected most conveniently using a three-roll calender. A sheet of the facing compound is placed in the mold and the fabric reinforcement with the backing layer calendered thereto is disposed over the facing compound to form the complete assembly. The mold is closed and the assembly is heated under pressure to effect vulcanization of the elastomeric compositions and, incidental therewith, the lamination of the various components of the printing plate. The vulcanization and molding together of the various Components of the printing plate normally is carried out at a temperature between 260 and 350 F. and at a pressure of from to 500 pounds per square inch.

The invention is illustrated by the drawing in which:

FIG. 1 is a perspective view of a printing plate constructed in accordance with this invention; and

FIG. 2 is a section on the line 2-2 of FIG. 1.

As shown in the drawing, the printing plate 10 comprises facing layer 11, a dimensionally stable fabric reinforcement 12 and a backing layer 13. The design to be printed (not shown) is embodied in the printing face 14 of facing layer 11. The printing plate 10 curls toward the backing layer 13 (as is clearly illustrated in FIG. 1) and thus inherently tends to assume the general contour of the cylindrical face of the plate cylinder of a rotary printing press.

A typical example of a printing plate constructed in accordance with this invention is as follows:

A woven glass fiber fabric is dipped into an aqueous dispersion of resorcinol, formaldehyde and neoprene latex of the following formulation:

Parts by Material: weight Neoprene latex (50% total solids) 200.0 Resorcinol 33.0

Formaldehyde 6.5 Caustic soda 0.5

Water 2700.0

and the adhesive coating thereby deposited on the fabric is dried.

The interstices of the fabric then are filled with an elastomeric composition of the following composition:

A backing layer 0.040 inch thick then is calendered onto one face of the fabric reinforcement. The backing layer composition may consist of the following formulation:

Parts by Material: weight Butadiene-acrylonitrile copolymer (Hyoar 1042 sold by The B. F. Goodrich Company) 100.0 Carbon black 100.0 Benzothiazyl disulfide 2.0 Sulfur 5.0 Tetramethylthiuram disulfide 0.2 Zinc oxide 5.0 Stearic acid 1.0 Dibutyl phthalate 10.0

The fabric reinforcement with backing layer calendered thereto is placed in a mold with the backing layer positioned against the mold face and a facing layer .060 inch thick is disposed upon the fabric layer; The facing layer may be formed of the following composition:

Parts by Material: weight Natural rubber 100.0

' Sulfur 2.5 Tetramethylthiuram disulfide 0.8 Zinc oxide 5.0 Carbon black 50.0 Stearic acid 2.0 Phenyl-beta-naphthylamine 1.5

The mold then is closed and is heated at 307 F. under a pressure of 450 pounds per square inch for a period of 12 minutes after which the mold is opened and the printing plate removed therefrom. As the printing plate cools to room temperature, it curls toward the backing layer thereof and away from the printing surface thereof.

The above example illustrates the use of different elastomers in the backing and facing layers of the printing plate. As mentioned above, the elastomer used in the backing and facing layers may be the same, a higher modulus composition for the backing layer being obtained through judicious compounding of the elastomer. Thus, the desired results are obtained when the natural rubber composition mentioned in-the above illustration is used in the facing layer and the following natural rubber composition is used for the backing layer composition:

Parts by Material: weight Natural 1'llbbI' 100.0 Carbon black 70.0 N-oxydiethylene benzothiazole 2-sulfenamide 2.0 Tetramethylthiuram monosulfide 0.25 Zinc oxide--- 40.0 Stearic acid 2.0 Sulfur 6.0 P-coumarone indene resin 4.0

Printing plates made in accordance with this invention have performed very successfully. Due to the inherent tendency of the printing plate to curl toward the backing layer, the printing plate naturally tends to conform to the cylindrical surface of the plate cylinder of a rotary printing press. Since the printing plate need not be distorted to any appreciable degree to cause it to conform to the curved surface of the plate cylinder of the printing press, there is no noticeable distortion of the design embodied in the printing surface of the printing plate.

Obvious variations of this invention may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A process for making a flexible printing plate which comprises placing in a mold a layer of vulcanizable elastomeric material for forming the facing layer of the printing plate, a dimensionally stable fabric reinforcing layer and a layer of vulcanizable elastomeric material for forming the backing layer of the printing plate with the said fabric reinforcing layer interposed between the two said layers of elastomeric material, the said layer of elastomeric material for forming the backing layer of the printing plate having a higher modulus than the said layer of elastomeric material for forming the facing layer of the printing plate, closing the mold, and heating the assembly comprised of the fabric reinforcing layer and the two said layers of elastomeric material under pressure to vulcanize the elastomeric materials in the said assembly and to bond the components of the said assembly into an integral structure.

2. A process for making a flexible printing plate which comprises placing in a mold a layer of vulcanizable elastomeric material for forming the facing layer of the printing plate, a dimensionally stable fabric reinforcing layer and a layer of vulcanizable elastomeric material for forming the backing layer of the printing plate with the said fabric reinforcing layer interposed between the two said layers of elastomeric material, the said layer of vulcanizable elastomeric material for forming the backing layer of the printing plate having been calendered onto the said fabric reinforcing layer before insertion into the said mold, the said layer of elastomeric material for forming the backing layer of the printing plate having a higher modulus than the said layer of elastomeric material for forming the facing layer of the printing plate, closing the mold, and heating the assembly comprised of the fabric reinforcing layer and the two said layers of elastomeric material under pressure to vulcanize the elastomeric materials in the said assembly and to bond the components of the said assembly into an integral structure.

3. A flexible printing plate comprising a facing layer of resilient elastomeric material, a backing layer of resilient elastomeric material, and a dimensionally stable fabric reinforcement interposed between said facing layer and said backing layer, said backing layer being formed of an elastomeric composition having a higher modulus than the elastomeric composition from which the facing layer is formed, said facing layer, fabric reinforcement and backing layer having been vulcanized together in a single molding operation, said printing plate being curled toward said backing layer whereby the printing plate assumes a curved contour which facilitates mounting the printing plate on the cylindrical face of the plate cylinder of a rotary printing press.

4. A flexible printing plate comprising a facing layer of resilient elastomeric material from 0.050 to 0.187 inch thick, a backing layer of resilient elastomeric material from 0.010 to 0.100 inch thick, and a dimensionally stable fabric reinforcement interposed between said facing layer and said backing layer, said backing layer being formed of an elastomeric composition having a higher modulus than the elastomeric composition from which the facing layer is formed, said facing layer, fabric reinforcement and backing layer having been vulcanized together in a single molding operation, said printing plate being curled toward said backing layer whereby the printing plate assumes a curved contour which facilitates mounting the printing plate on the cylindrical face of the plate cylinder of a rotary printing press.

5. A flexible printing plate comprising a facing layer of resilient elastomeric material, a backing layer of resilient elastome ric material, and a woven glass fiber reinforcing layer interposed between said facing layer and said backing layer, said backing layer being formed of an elastomeric composition having a higher modulus than the elastomeric composition from which the facing layer is formed, said facing layer, reinforcing layer and backing layer having been vulcanized together in a single molding operation, said printing plate being curled toward said backing layer whereby the printing plate assumes a curved contour which facilitates mounting the printing plate on the cylindrical face of the plate cylinder of a rotary printing press.

6. A flexible printing plate comprising a facing layer of resilient elastomeric material from 0.050 to 0.187 inch thick, a backing layer of resilient elastomeric material from 0.010 to 0.100 inch thick, and a woven glass fiber reinforcing layer interposed between said facing layer and said backing layer, said backing layer being formed of an elastomeric composition having a higher modulus than the elastomeric composition from which the facing layer is formed, said facing layer, reinforcing layer and backing layer having been vulcanized together in a single molding operation, said printing plate being curled toward said backing layer whereby the printing plate assumes a curved contour which facilitates mounting the printing plate on the cylindrical face of the plate cylinder of a rotary printing press.

7. A flexible printing plate comprising a facing layer of resilient elastomeric material, a backing layer of resilient elastomeric material, and a dimensionally stable fabric 8 reinforcement interposed between said facing layer and said backing layer, said backing layer being formed of an elastomeric composition having a, higher modulus than the elastomeric composition from which the facing layer is formed, said facing layer being of a greater thickness than said backing layer, said facing layer, fabric reinforceincnt and backing layer having been vulcanized together in a single molding operation, said printing plate being curled toward said backing layer whereby the printing plates assumes a curved contour which facilitates mounting the printing plate on the cylindrical face of the plate cylinder of a rotary printing press.

8. A flexible printing plate comprising a facing layer of resilient elastomeric material, a backing layer of resilient elastomeric material, and a'woven glass fiber reinforcing layer interposed between said facing layer and said backing layer, said backing layer being formed of an elastomeric composition having a higher modulus than the elastomeric composition from which the facing layer is formed, said facing layer being of a greater thickness than said backing layer, said facing layer, fabric reinforcement and backing layer having been vulcanized together in a single molding operation, said printing plate being curled toward said backing layer whereby the printing plate assumes a curved contour which facilitates mounting the printing plate on the cylindrical face of the plate cylinder of a rotary printing press.

References Cited in the file of this patent UNITED STATES PATENTS 

3. A FLEXIBLE PRINTING KPLATE COMPRISING A FACING LAYER OF RESILIENT ELASTOMERIC MATERIAL, A BACKING LAYER OF RESILIENT ELASTOMERIC MATERIAL, AND A DIMENSIONALLY STABLE FABRIC REINFORCEMENT INTERPOSED BETWEEN SAID FACING LAYER AND SAID BACKING LAYER, SAID BACKING LAYER BEING FORMED OF AN ELASTOMERIC COMPOSITION HAVING A HIGHER MODULUS THAN THE ELASTOMERIC COMPOSITION FROM WHICH THE FACING LAYER IS FORMED, SAID FACING LAYER, FABRIC REINFORCEMENT ADVANCE THE THREADS INTERMITTENTLY THROUGH THE MACHINE, COMBS GUIDING THE TENSIONED THREADS AT A PREDETERMINED SPACING, A MOVABLE BELT INCLUDING A RETILINEAR STRAND OVER WHICH THE THREADS ARE ADAPTED TO PASS, MEANS FOR APPLYING A LAYER OF SIZING ONTO SAID BELT, MEANS FOR ENGAGING SAID THREADS AFTER THE SAME HAVE PASSED THROUGH SAID COMBS TO URGE THE THREADS ONTO THE BELT WITH THE SIZING THEREON WHEREBY SAID THREADS ADHERE TO SAID BELT, FRAMES CARRYING DYESTUFFS AND INCLUDING A SHEET STENCILED IN ACCORDANCE WITH A PREDETERMINED PATTERN, SAID FRAMES BEING ADAPTED TO BE URGED AGAINST THE THREADS PASSING OVER THE RECTILINEAR BELT STRAND TO IMPRESS THE SAME THROUGHTOUT WITH DYESTUFFS, A DRYING CHAMBER FOR THE PRINTED WARP THREADS PASSING OFF SAID RECTILINEAR BELT STRAND, AND AT LEAST ONE OUTPUT COMB SPACING THE SIZED, PRINTED AND DRIED WARP THREADS AND GUIDING THEM ONTO THE WARP BEAM OF THE WEAVING LOOM. 